This chapter focuses on the diagnosis and management of patients with adult congenital heart disease (CHD). The role of transesophageal echocardiography (TEE) during the percutaneous procedure is to identify the number of defects and monitor the implantation of the transcatheter device. This must be done without obstructing fluoroscopy. During implantation the location of catheters, balloon sizing, and the position of the device both before and after release should be assessed. TEE guidance during transcatheter closure of atrial septal defect (ASD), patent foramen ovale (PFO), and ventricular septal defect (VSD) is now standard practice. TEE is currently considered the reference standard for PFO diagnosis, allowing direct imaging of the interatrial septum and saline contrast shunting through a PFO. Possible partial atrioventricular septal defect (AVSD) should be considered in patients who have complex patterns of mitral regurgitation (MR).